package bma.common.langutil.core;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.zip.CRC32;

public enum HashAlgorithm {

	  /**
	   * Native hash (String.hashCode()).
	   */
	  NATIVE_HASH,
	  /**
	   * CRC_HASH as used by the perl API. This will be more consistent both
	   * across multiple API users as well as java versions, but is mostly likely
	   * significantly slower.
	   */
	  CRC_HASH,
	  /**
	   * FNV hashes are designed to be fast while maintaining a low collision rate.
	   * The FNV speed allows one to quickly hash lots of data while maintaining a
	   * reasonable collision rate.
	   *
	   * @see <a href="http://www.isthe.com/chongo/tech/comp/fnv/">fnv
	   *      comparisons</a>
	   * @see <a href="http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash">fnv at
	   *      wikipedia</a>
	   */
	  FNV1_64_HASH,
	  /**
	   * Variation of FNV.
	   */
	  FNV1A_64_HASH,
	  /**
	   * 32-bit FNV1.
	   */
	  FNV1_32_HASH,
	  /**
	   * 32-bit FNV1a.
	   */
	  FNV1A_32_HASH,
	  /**
	   * MD5-based hash algorithm used by ketama.
	   */
	  KETAMA_HASH;

	  private static final long FNV_64_INIT = 0xcbf29ce484222325L;
	  private static final long FNV_64_PRIME = 0x100000001b3L;

	  private static final long FNV_32_INIT = 2166136261L;
	  private static final long FNV_32_PRIME = 16777619;

	  private static MessageDigest md5Digest = null;

	  static {
	    try {
	      md5Digest = MessageDigest.getInstance("MD5");
	    } catch (NoSuchAlgorithmException e) {
	      throw new RuntimeException("MD5 not supported", e);
	    }
	  }

	  /**
	   * Compute the hash for the given key.
	   *
	   * @return a positive integer hash
	   */
	  public long hash(final String k) {
	    long rv = 0;
	    int len = k.length();
	    switch (this) {
	    case NATIVE_HASH:
	      rv = k.hashCode();
	      break;
	    case CRC_HASH:
	      // return (crc32(shift) >> 16) & 0x7fff;
	      CRC32 crc32 = new CRC32();
	      crc32.update(getKeyBytes(k));
	      rv = (crc32.getValue() >> 16) & 0x7fff;
	      break;
	    case FNV1_64_HASH:
	      // Thanks to pierre@demartines.com for the pointer
	      rv = FNV_64_INIT;
	      for (int i = 0; i < len; i++) {
	        rv *= FNV_64_PRIME;
	        rv ^= k.charAt(i);
	      }
	      break;
	    case FNV1A_64_HASH:
	      rv = FNV_64_INIT;
	      for (int i = 0; i < len; i++) {
	        rv ^= k.charAt(i);
	        rv *= FNV_64_PRIME;
	      }
	      break;
	    case FNV1_32_HASH:
	      rv = FNV_32_INIT;
	      for (int i = 0; i < len; i++) {
	        rv *= FNV_32_PRIME;
	        rv ^= k.charAt(i);
	      }
	      break;
	    case FNV1A_32_HASH:
	      rv = FNV_32_INIT;
	      for (int i = 0; i < len; i++) {
	        rv ^= k.charAt(i);
	        rv *= FNV_32_PRIME;
	      }
	      break;
	    case KETAMA_HASH:
	      byte[] bKey = computeMd5(k);
	      rv = ((long) (bKey[3] & 0xFF) << 24)
	          | ((long) (bKey[2] & 0xFF) << 16)
	          | ((long) (bKey[1] & 0xFF) << 8)
	          | (bKey[0] & 0xFF);
	      break;
	    default:
	      assert false;
	    }
	    return rv & 0xffffffffL; /* Truncate to 32-bits */
	  }

	  /**
	   * Get the md5 of the given key.
	   */
	  public static byte[] computeMd5(String k) {
	    MessageDigest md5;
	    try {
	      md5 = (MessageDigest) md5Digest.clone();
	    } catch (CloneNotSupportedException e) {
	      throw new RuntimeException("clone of MD5 not supported", e);
	    }
	    md5.update(getKeyBytes(k));
	    return md5.digest();
	  }
	  
	  /**
	   * Get the bytes for a key.
	   *
	   * @param k the key
	   * @return the bytes
	   */
	  public static byte[] getKeyBytes(String k) {
	    try {
	      return k.getBytes("UTF-8");
	    } catch (UnsupportedEncodingException e) {
	      throw new RuntimeException(e);
	    }
	  }

	  /**
	   * Get the keys in byte form for all of the string keys.
	   *
	   * @param keys a collection of keys
	   * @return return a collection of the byte representations of keys
	   */
	  public static Collection<byte[]> getKeyBytes(Collection<String> keys) {
	    Collection<byte[]> rv = new ArrayList<byte[]>(keys.size());
	    for (String s : keys) {
	      rv.add(getKeyBytes(s));
	    }
	    return rv;
	  }
	  
	
}
